The invention relates to an optoelectronic measuring device for monitoring combustion processes in the combustion chamber of an internal combustion engine during operation, with optical sensors assigned to the combustion chamber, which are connected to an evaluation unit, the sensor ends on the side of the combustion chamber being essentially positioned in a plane and the sensors being aligned so that the individual viewing angles of the sensors will uniformly cover at least one predefined measuring sector of the combustion chamber.
For engine development it is of prime importance to understand t h e development of combustion processes in time and space. In EP 0 593 413 B1 an optoelectronic measuring device is described where the sensors are located in the cylinder head gasket of an internal combustion engine. In order to produce a two-dimensional image of the combustion processes the sensors are arranged such that their individual viewing angles will uniformly cover the area of the combustion chamber in the plane of the cylinder head gasket. The evaluation unit is provided with a computing unit which will process the signals of the individual sensors to compute brightness values for defined areas of the cylinder head gasket plane and convert them into a two-dimensional image. In this way measurements can be obtained without interfering with the engine or geometry of the combustion chamber. Since the sensors are integrated in the cylinder head gasket, a separate sensor-carrying cylinder head gasket is required for each engine. Another drawback is that the cylinder head must be removed whenever a cylinder head gasket is to be replaced by a sensor-carrying cylinder head gasket. For this reason optical measurement by means of a sensor-carrying cylinder head gasket is complex and cost-intensive.
U.S. Pat. No. 4,393,687 A is concerned with a sensor arrangement for determining oscillations arising upon knocking of a combustion engine, which includes one or more optical receivers in the combustion chamber, preferably configured as a glass rod or a lightguide cable of glass fibers. The optical receivers are either integrated in the spark plug, or connected to a pre-chamber, or inserted in the cylinder head gasket.
The spark plugs for combustion engines described in U.S. Pat. No. 4,446,723 A and U.S. Pat. No. 4,505,186 A are provided with a centrally positioned single lightguide. This will only permit simple measurements, however, such as determining whether or not engine knocking occurs. For the more complex measurements, such as monitoring the development of an inner flame cone or its movement, spark plugs with a single lightguide will not be sufficient.
From AT 002 228 U1 a spark plug is known which is provided with several lightguides ending in the combustion chamber, which permit complex measurements such as monitoring flame propagation, in addition to knock detection. In that instance the sensor ends are arranged in a ring on the end face of the spark plug facing the combustion chamber. This will allow monitoring of combustion phenomena only within a cylindrical or cone-shaped measuring area. Processes in the area of the top or at the periphery of the combustion chamber cannot be covered in this manner.
It is an object of this invention to overcome the disadvantages of known devices and to improve an opto-electronic measuring device of the above type in such a way that the costs of production and measuring will be reduced.
According to the invention this object is achieved by providing that the optical sensors be located in an essentially cylindrical component projecting into the combustion chamber and the sensor ends be located essentially radially along the wall of the component. The component carrying the optical sensors is screwed into the cylinder head via a bore for a functional part ending in the combustion chamber or a separate sensor bore. The component may be formed by a spark plug or an injector. In this case no further measuring bores will be required in the combustion chamber. The cylindrical wall could also be configured as a separate sensor part. The sensor ends located in the wall are directed into the combustion chamber more or less radially, resulting in an essentially plane or umbrella-shaped measuring sector.
As the optical sensors are located in the functional component no modifications of the engine will be necessary, and the operating range (speed and load) of the engine will not be restricted. The signals of the individual sensors can be converted into two-dimensional images by means of algorithms known from emission tomography, the resolution of the images being limited only by the number of sensors used. In a proven variant of the invention eight sensors are used per component. The measuring device of the invention will ensure prolonged tests of combustion processes with temporal and spatial resolution using standard electronic components.
It has proved to be of particular advantage if each optical sensor is provided with a deflector element at its end. The optical fibers of the sensors are guided towards the deflector element essentially in parallel with the longitudinal axis of the component. Due to the deflector element, the viewing direction of the optical fibers is deflected by 90xc2x0 in radial direction, such that an area of the combustion chamber surrounding the wall of the component may be monitored. The deflector element can be configured as a mirror or prism, preferably a sapphire prism, and can be attached to the lower end of the optical fibers. According to a variant characterized by manufacturing ease, the deflector element is configured as a ring.
In further development of the invention each optical sensor is provided with a bundle of optical fibers. This permits full coverage of a measuring sector surrounding the cylindrical wall of the component. To increase spatial resolution, it is recommended to reduce the viewing angle of the optical fibers. This may be achieved by providing an aperture at the end of at least one optical fiber. Spatial resolution may also be achieved by means of self-focusing end faces of the glass fibers.
In an especially advantageous variant of the invention the end of at least one optical fiber is located in the focal plane of a lens to introduce more light into the fiber. It is also possible to arrange the ends of several lightguides in the focal plane of the lens, preferably in rows of five fibers, for example. The spatial resolution, especially in the direction of the circumference of the component, may be significantly increased by positioning at least one row of fiber ends essentially in a circular arc or tangent line relative to the component.
No separate lens will be required if the deflector element is configured as a lens. The deflector element could also exhibit a curved optical boundary surface with the combustion chamber, which should be configured as a lens, and preferably as a first cylinder lens. In this way each optical fiber can be assigned a certain viewing angle.
According to a preferred variant of the invention the deflector element exhibits a curved deflector surface configured as a lens, and preferably as a second cylinder lens. In this way a plurality of measuring sectors may be obtained one above the other in the direction of the longitudinal axis of the component, and the quality of measurement may be significantly improved. A plurality of measuring sectors in the direction of the longitudinal axis of the component could also be obtained by providing the deflector element with a deflector surface configured as section of a torus, the deflector element being preferably constituted by a sapphire pin. High-quality measuring results will be obtained if the curvature radius of the curved deflector surface is greater than that of the curved optical boundary surface.
In order to obtain a plurality of measuring sectors in a simple way it is of advantage if the ends of at least two optical fibers per sensor are placed at different distances from a mean longitudinal axis of the component. The fiber ends may be arranged in rows, preferably in at least two rows that are essentially parallel with each other. At least two rows could also be aligned orthogonally to each other. Spatial resolution in the direction of the longitudinal axis of the component is significantly increased by positioning at least one row of fiber ends essentially radially relative to the component.
The light rays arrive at the deflector element via the curved optical boundary surface, and are collimated by the first cylinder lens and reflected at the curved deflector surface. Due to the deflector surface configured as a second cylinder, lens rays from several measuring sectors are picked up and passed on at different reflection angles to the rows of fiber ends arranged in different tangential and radial alignments.
For conversion into two-dimensional images, a plurality of measuring devices is provided for each combustion chamber, which are preferably located inside separate components. Preferably, each measuring device exhibits at least forty directions of vision evenly distributed over the circumference. The measuring sectors of the individual components may partly overlap, or cover different areas of the combustion chamber, for example, different measuring planes.
The measuring device of the invention will enable the location of knocking combustion to be detected in a simple way, by evaluation of the light signals of the combustion process monitored. A single measuring device per cylinder will suffice for localization of the engine knock. As knocking, i.e., an uncontrolled self-ignition of spark-ignited fuels, may be interpreted as shock waves, which can be described in mathematical terms as spherical waves being a function of intensity distribution and propagation rate, a simple evaluation and computation is possible from which the origin of knocking combustion can be inferred. The shock wave of a knock will only be registered by the sensors when the wave front enters the measuring sector of the combustion chamber. From the values measured for the wave front by means of the optical sensors, the point of origin of the wave front may be inferred with the use of a mathematical model describing the shock wave.
It would further be possible to employ the optical measuring device together with a pressure sensor, and to use the difference in propagation time between sound wave and light wave to precisely determine the distance of the knocking location from the pressure sensor, and thus, in combination with the optical measurement, the original location of the engine knock.